It would be absurd if they could be _forced_ to globally adopt an EU regulation, but I think not as much if they _do_ globally adopt this EU regulation, for two reasons:
1. There might be significant internal hassle involved in working with more than one standard of integrity within a single company dealing with integrity as its currency and user base as pillars. It may be easier for them to just use a common one even if it is more restrictive, at least if it is backed by a population of 500 million people.
2. Facebook are going through a PR crisis and need to dig out of that hole somehow. If they only adopt EU regulations in the EU, it could be seen as Facebook are only doing the least they can to protect the integrity of their users and that this is seen as a better move?
It's funny how GDPR coincides with the Facebook scandals as of late, though... Their lawyers and engineers have got to be buried with work. I can't even begin to imagine what a company of Facebook's scale and business model need to do to support GDPR globally.